Contamination monitoring system

ABSTRACT

A contamination monitoring system having a portable framework which carries a rinsing bath for detachable connection to a remote fluid source. A transport structure is mounted on the framework to accommodate transport of the system to and from the remote fluid source. The framework includes a chamber which encloses the rinsing bath to isolate it from the surrounding environment, typically using a filter which removes unwanted particles from air within the chamber. The filter also typically creates a vertical airflow within the chamber. In one embodiment, the system employs a rinsing bath with inner and outer tanks, the inner tank being configured to hold wafers to be rinsed and the outer tank being configured to hold the inner tank. An input port introduces fluid from the remote fluid source into the inner tank for overflow into the outer tank. The outer tank employs an output port for discharge of fluid received from the inner tank. The system identifies contaminated fluid using a test wafer which is cleansed within the rinsing bath and compared to a wafer having optimal characteristics. The source of contamination may be identified by connecting the rinsing bath to various outputs along the fluid path from the remote fluid source, which effectively allows the user to identify an affected fluid path segment.

This is a continuation of application Ser. No. 08/995,775, filed Dec.22, 1997, and now U.S. Pat. No. 5,849,103.

TECHNICAL FIELD

The present invention relates generally to a system for monitoringcontamination of fluid used to rinse crystal wafers, and moreparticularly, to a system employing methodology whereby a source ofcontamination of fluid received from a remote fluid source may beidentified.

BACKGROUND

The production of crystal wafers typically involves cleaning a waferwith an alkali or acid solution, and then rinsing the wafer withpurified water so as to remove the solution and any contaminants whichhave found their way onto the wafer. This cleansing heretofore hasinvolved a series of tanks, each of which is flushed with purified waterwhich rinses any wafer (or wafers) contained within the tank. In such asystem, wafers are moved from one tank to the next, each successive tankbeing configured to further cleanse the wafers of any residual solutionor contaminants.

Unfortunately, known wafer rinsing systems do not ensure that the waterfor rinsing the crystal wafers is adequately purified, and thus do notensure that resultant crystal wafers are free from defects. Accordingly,it would be useful to provide a system whereby water used to rinse thewafers may be monitored to identify any contamination of the suppliedwater, and if such contamination does exist, to identify the location ofthe contamination source.

DISCLOSURE OF THE INVENTION

The aforementioned goals and objectives are met by providing acontamination monitoring system having a portable framework whichcarries a rinsing bath for detachable connection to a remote fluidsource. The rinsing bath includes an input port which detachablyconnects to the remote fluid source to receive fluid for passage overthe crystal wafers contained within the rinsing bath. A transportstructure is mounted on the framework to accommodate transport of thesystem to and from the remote fluid source.

The framework includes a chamber which encloses the rinsing bath toisolate it from the surrounding environment, typically using a filterwhich removes unwanted particles from air within the chamber. The filteralso typically creates a vertical airflow within the chamber.

In one embodiment, the system employs a rinsing bath with inner andouter tanks, the inner tank being configured to hold wafers to be rinsedand the outer tank being configured to hold the inner tank. The inputport introduces fluid from the remote fluid source into the inner tankfor overflow into the outer tank. The outer tank employs an output portfor discharge of fluid received from the inner tank.

The system identifies contaminated fluid using a test wafer which iscleansed within the rinsing bath and compared to a wafer having optimalcharacteristics. As will be understood, this is accomplished by a methodinvolving the steps of (1) placing a test wafer in a rinsing bath; (2)connecting the input port of the rinsing bath to an output of the remotefluid source; (3) passing fluid from the remote fluid source to therinsing bath through the input port; (4) removing the test wafer fromthe rinsing bath; and (5) comparing the removed test wafer to an optimalwafer, a predetermined difference between the test wafer and the optimalwafer being indicative of contamination of the remote fluid source.

Furthermore, the source of contamination may be identified by connectingthe rinsing bath to various outputs along the fluid path from the remotefluid source, and repeating the passing, removing and comparing stepsupon connection to each output. This effectively allows the user toidentify an affected fluid path segment.

These and other objects and advantages of the present invention will bemore readily understood after a consideration of the drawings and thedetailed description of the preferred embodiment which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a contamination monitoring systemconstructed in accordance with the present invention, the monitoringsystem being used in connection with a remote fluid source with one ormore fluid outputs.

FIG. 2 is a fragmentary isometric view of the wafer rinsing cart shownin FIG. 1, a portal being opened to expose a rinsing bath wherein wafersare cleansed.

FIG. 3 is a rear view of the wafer rinsing cart shown in FIG. 1.

FIG. 4 is a flowchart showing a method of identifying contamination offluid received from a remote fluid source for use in rinsing crystalwafers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND BEST MODE OFCARRYING OUT THE INVENTION

FIGS. 1 through 3 depict a contamination monitoring system in the formof a cart 10 configured for use in rinsing wafers with fluid (e.g.,purified water) received from a remote fluid source 20. As indicated,the fluid typically is supplied to the cart using a hose 22, the hosebeing configured to connect to any of various outputs (20a, 20b) along afluid path of the remote fluid source. Although only two outputs areshown, those skilled will recognize that the fluid path may take theform of an elongate conduit with multiple fluid segments extendingthrough various areas of a manufacturing or testing facility.

Cart 10 includes a transport structure 12 which allows cart 10 to beeasily transportable to any of the various outputs (20a, 20b), thetransport structure typically taking the form of a wheeled lowerframework. In the depicted embodiment, the lower framework includes aplurality of frame members 14 assembled such that transport structure 12has a generally rectangular shape. Wheels 16 are mounted at the base ofthe transport structure. A handle 18 is attached to the transportstructure to allow an operator to maneuver cart 10 to a desiredlocation.

Mounted atop transport structure 12 is a generally rectangular upperframework 30 which is constructed from a plurality of frame members 32.Frame members 14 and 32 are typically made of stainless steel hollowtubing, but may be formed from any suitably strong material flee fromcontamination. Frame members 14 and 32 are welded or otherwise attachedto each other.

Upper framework 30 also includes a chamber 34 defined by front wall 40,side walls 48, rear wall 50, top 58 and bottom 62, all of which areattached to upper framework 30 and preferably made of polypropylene.Chamber 34 encloses a workspace 36 and isolates workspace 36 from theenvironment in which cart 10 is located. Front wall 40 has a front door42 mounted on hinges 44. An operator opens and closes front door 42using a handle 46. Front wall 40 and front door 42 preferably aretransparent. Rear wall 50 has a plurality of vents 52. Vent doors 54slide horizontally on tracks 56 and can be opened and closed to regulatethe amount of purified air flowing outwardly through vents 52. Anoperator opens and closes vent doors 54 using handles 57.

An air filter 60, preferably a HEPA filter, is mounted on top 58 influid communication with chamber 34. When filter 60 is running properlyand vent doors 54 are opened, purified air is forced into workspace 36and out vents 52. This constant vertically downward flow of purified aircreates a clean area in workspace 36 wherein wafer cleansing and testingfor contaminants can be performed. Filter 60 can be of any type known inthe semiconductor manufacturing industry and will not be furtherdescribed.

A rinsing bath 70 is defined within workspace 36, the rinsing bath beingconfigured for selected receipt of purified water via a water inlet 72.The water inlet extends through one of side walls 48 or bottom 62 andincludes a valve 74 for selectively allowing water to enter workspace36. A flow meter 76 is connected, on one side, to valve 74 whichregulates the water flow into workspace 36. The other side of flow meter76 is connected to a spout 78 which directs water into an inner tank 80,which preferably is made of quartz and has an open top 81. Fluid may befed to inner tank 80 either from above or from below, and is configuredso as not to disturb the contents of the inner tank. As indicated, theinner tank is disposed within chamber 34, which defines an outer tank82. An outlet 64 is defined in bottom 62 and is adapted to drain fluidfrom the outer tank. A valve 66 selectively opens and closes outlet 64.A shelf 84 is situated within the workspace at an elevation above innertank 80. The typical shelf has a plurality of perforations (not shown)which contribute to flow of air within the workspace.

The wafer rinsing process will now be described. Cart 10 is moved viatransport structure 12 to a selected output of remote fluid source 20.Hose 22, communicating with an output such as 20a, is connected to inlet72. Valve 74 is opened so that fluid flows through valve 74 whichregulates via flow meter 76. Fluid flows out of spout 78 into inner tank80. When fluid fills inner tank 80, the fluid flows out over open top 81and into outer tank 82. The fluid is drained from outer tank 82 throughoutlet 64.

Once the inner tank is filled, an operator opens front door 42 andplaces one or more crystal wafers such as test wafer 90 into inner tank80. The test wafer 90 is enclosed in a teflon cassette 92. When testwafer 90 is fully rinsed (as determined by duration of rinse time, or byquantity of fluid flow), the cassette is placed in a sealable box 94 fortransport to a testing site. The wafer then is removed from the innertank for testing to determine the purity level of the fluid. This can bedone by comparing the characteristics of test wafer 90 to an optimalwafer (e.g., a wafer which is known to have been rinsed inuncontaminated water). The difference between the two wafers indicatesthe level of contamination of remote fluid source 20 at output 20a.Suitable wafer quality tests useable with the present invention includevapor phase decomposition, minority carrier recombination lifetime,TXRF, and SIMS, all of which are known in the industry. Valve 66 is thenopened so that fluid is drained out of outer tank 82 through outlet 64.Inlet 72 is disconnected from output 20a, and cart 10 can be moved toanother output (e.g., 20b) to repeat the wafer rinsing process asdesired. Using this repetitive testing, it is possible to identify thesource of contamination within the flow path by identifying the point atwhich contamination of the test water is eliminated.

A method of identifying contaminated fluid using a test wafer accordingto the present invention is shown in flowchart form in FIG. 4. In step100, test wafer 90 is placed in rinsing bath 70. In step 102, inlet 72is connected to an output port 20a of remote fluid source 20. In step104, fluid is passed from remote fluid source 20, through inlet 72, torinsing bath 70. In step 106, test wafer 90 is removed from rinsing bath70. In step 108, test wafer 90 is compared to an optimal wafer, in whicha predetermined difference in characteristics between test wafer 90 andthe optimal wafer being indicative of contamination of the remote fluidsource. Such characteristics may include, for example, electricalcharacteristics, chemical characteristics, or the like. If desired, theprocess can be repeated at different outputs (e.g., 20b, . . . 20n) asshown by step 110.

As demonstrated in the above description, the present invention providesa contamination monitoring system useable in any environment. Filter 60forces air through vents 52 and ensures a purified airflow withinworkspace 36. When an operator opens front door 42, workspace 36 remainssubstantially contaminant-free due to the purified airflow regardless ofthe contamination level of the surrounding environment.

The wafer comparison technique of the present invention allows for moreprecise and accurate measurement of contamination than conventionalmethods of measuring the water directly. In addition, the presentinvention provides for more accurate contamination testing because thewafer rinsing process simulates conditions present in the manufacturingprocesses.

The present invention is not limited to use in determining contaminationlevels in rinsing fluid. The present invention could also be used tofocus exclusively on the effects of the rinsing fluid on wafers.Alternatively, the present invention could be used to assist inevaluating different ion-exchange resins.

The present invention can also have application in the medical,pharmaceutical, biotechnological, food preparation, aerospace, and otherprocessing industries where a portable clean area is necessary to testfor contaminants or to protect objects from contamination.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed, and many modifications and variations are possible inlight of the above teaching. The embodiments were chosen and describedin order to best explain the principles of the invention and itspractical application to thereby enable others skilled in the art tobest utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto.

We claim:
 1. A system for use in monitoring contamination of fluidreceived from a remote fluid source to rinse one or more crystal wafers,the system comprising:a portable framework including a chamber whichencloses a workspace to isolate the workspace from an environment inwhich the system is located; a rinsing bath mounted within the chamberand configured to receive the one or more crystal wafers for rinsing,the rinsing bath having an input port which detachably connects to theremote fluid source to receive fluid for passage over the crystalwafers; a cassette configured to support the one or more crystal wafersin the rinsing bath; a sealable container configured to receive the oneor more crystal wafers after the one or more crystal wafers are rinsedso that the wafers may be transported from the chamber; a transportstructure mounted on the framework to accommodate transport of thesystem to and from the remote fluid source; and a wafer-qualitymeasurement apparatus configured to test one or more characteristics ofa rinsed crystal wafer for comparison with an optimal wafer, anydifference in the one or more characteristics being indicative ofcontamination of the fluid received from the remote fluid source.
 2. Thesystem of claim 1 which further comprises a filter operatively mountedon the framework in communication with the chamber to filter airentering the workspace from the environment.
 3. The system of claim 2,wherein the filter creates a vertical airflow within the workspace. 4.The system of claim 1, wherein the chamber defines an adjustable vent tothe environment.
 5. The system of claim 1, wherein the chamber defines asealable portal between the workspace and the environment.
 6. The systemof claim 1, wherein the chamber is made of polypropylene.
 7. The systemof claim 1, wherein the rinsing bath includes an inner tank which holdswafers to be rinsed, and an outer tank which holds the inner tank, theinput port being configured to introduce fluid from the remote fluidsource into the inner tank for overflow into the outer tank.
 8. Thesystem of claim 7, wherein the outer tank has an output port fordischarge of fluid received from the inner tank.
 9. The system of claim7, wherein the inner tank is made of quartz.
 10. The system of claim 1,wherein the transport structure is a wheeled cart.
 11. The system ofclaim 1, where the chamber includes a bottom and a drain positioned inthe bottom so that fluid overflowing the rinsing bath flows to thebottom of the chamber and out the drain.
 12. The system of claim 1,further comprising a flow meter associated with the input port toregulate the flow of fluid into the rinsing bath.
 13. The system ofclaim 1, further comprising a shelf within the chamber configured tosupport the sealable container.
 14. The system of claim 1, furthercomprising vents in the chamber configured to allow air to flowoutwardly from the chamber.
 15. The system of claim 1, furthercomprising a handle attached to the transport structure.